Pancreases from neonatal mice, rats and humans will be isolated, dispersed, and cultured under conditions previously demonstrated suitable for long-term maintenance of beta cells. These conditions will be modified to support maintenance of viable beta cells for progressively longer periods until a beta cell bank can be established. During this period, beta cell cultures will be assessed by light and electron microscopy for morphological changes. Physiological maturation will be assessed by basal and stimulated insulin secretion. Simultaneously, membrane insulin receptors of cultured and cryopreserved beta cells are to be defined and characterized. Further, physiological correlates of receptor activity are to be sought. It is anticipated that data from these investigations will provide insight into the mechanisms of insulin secretion and provide a basis for the establishment of a beta cell bank to serve as a source of material for investigations in other biomedical fields. Further, there is a potential that these cells may become a source of donor tissue for future transplantation in diabetic man.